In detached leaf tests on faba bean (Vicia faba L.), genotypes partially resistant and susceptible to Botrytis
fabae were examined. Expression of four components of partial resistance to a virulent isolate of B. fabae differed
depending on the plant age and the leaf age of the genotypes. The incubation period of resistant genotypes at the
podding stage was longer than that of susceptible genotypes at the same stage. The area under disease progress
curve (AUDPC) of the lesion size increased from the seedling to the flowering stage but declined at the podding stage
in all genotypes. Differences between resistant and susceptible genotypes for lesion size were significant except on
old leaves from plants at the podding stage. The latent period decreased, and spore production increased with increasing
growth and leaf age but there was significant interaction with the genotype. These last two components of
partial resistance were more clearly expressed at all growth stages on FRY167 (highly resistant) but were expressed
only at the seedling and podding stages on FRY7 (resistant). The resistant line BPL710 was not significantly different
from the susceptible genotypes for the latent period at any growth stage, and for spore production at the seedling
and flowering stages. Leaf age affected all genotypes, but with a significant interaction between leaf age and growth
stage. Components of partial resistance were more strongly expressed on young leaves from plants at the seedling or
flowering stage